linux-kernel - Re: [PATCH 3/5] crypto: ccp: Play nice with vmalloc'd memory for SEV command structs

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Date:   Mon, 5 Apr 2021 11:01:20 -0500
From:   Brijesh Singh <brijesh.singh@....com>
To:     Sean Christopherson <seanjc@...gle.com>,
        Christophe Leroy <christophe.leroy@...roup.eu>
Cc:     brijesh.singh@....com, Paolo Bonzini <pbonzini@...hat.com>,
        Tom Lendacky <thomas.lendacky@....com>,
        John Allen <john.allen@....com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-crypto@...r.kernel.org, linux-kernel@...r.kernel.org,
        Borislav Petkov <bp@...e.de>
Subject: Re: [PATCH 3/5] crypto: ccp: Play nice with vmalloc'd memory for SEV
 command structs


On 4/5/21 10:06 AM, Sean Christopherson wrote:
> On Sun, Apr 04, 2021, Christophe Leroy wrote:
>> Le 03/04/2021 à 01:37, Sean Christopherson a écrit :
>>> @@ -152,11 +153,21 @@ static int __sev_do_cmd_locked(int cmd, void *data, int *psp_ret)
>>>   	sev = psp->sev_data;
>>>   	buf_len = sev_cmd_buffer_len(cmd);
>>> -	if (WARN_ON_ONCE(!!data != !!buf_len))
>>> +	if (WARN_ON_ONCE(!!__data != !!buf_len))
>>>   		return -EINVAL;
>>> -	if (WARN_ON_ONCE(data && is_vmalloc_addr(data)))
>>> -		return -EINVAL;
>>> +	if (__data && is_vmalloc_addr(__data)) {
>>> +		/*
>>> +		 * If the incoming buffer is virtually allocated, copy it to
>>> +		 * the driver's scratch buffer as __pa() will not work for such
>>> +		 * addresses, vmalloc_to_page() is not guaranteed to succeed,
>>> +		 * and vmalloc'd data may not be physically contiguous.
>>> +		 */
>>> +		data = sev->cmd_buf;
>>> +		memcpy(data, __data, buf_len);
>>> +	} else {
>>> +		data = __data;
>>> +	}
>> I don't know how big commands are, but if they are small, it would probably
>> be more efficient to inconditionnally copy them to the buffer rather then
>> doing the test.
> Brijesh, I assume SNP support will need to copy the commands unconditionally? If
> yes, it probably makes sense to do so now and avoid vmalloc dependencies
> completely.  And I think that would allow for the removal of status_cmd_buf and
> init_cmd_buf, or is there another reason those dedicated buffers exist?


Yes, we need to copy the commands unconditionally for the SNP support.
It makes sense to avoid the vmalloc dependencies. I can't think of any
reason why we would need the status_cmd_buf and init_cmd_buf after those
changes.